There is no effective therapy for hormone refractory prostate cancer. Several characteristics of monoclonal antibodies (mAbs) are particularly well suited for the demands of prostate cancer therapy. mAb Prost 30 binds specifically with a prostate related antigen. The investigators wish to define the toxicity and preliminary efficacy of 131 Iodine-mAb Prost 30 in patients with hormone refractory prostate cancer. Progress report and summary of findings: Seven patients have entered and completed the study. Three of those patients were treated at dose level 30mCi/m2 and four were treated at dose level 45mCi/m2. A decline in serum PSA was observed in 2 patients. Three of those patients treated at a dose level of 45mCi/m2 experienced a grade 3 neutropenia and/or thrombocytopenia (2 patients). The toxicity experienced may be a result of prior radioation treatment in the form of XRT (3 patients) and or 89 Strontium (1 patient). The protocol was modified to exclude patients with prior external beam radiation to major bone marrow bearing sites and patients who have received Strontium. Three of the seven patients treated have died of metastatic prostate cancer.